Photographic cameras have been in widespread use for quite some time. Basically, such a camera operates by exposing a portion of a light sensitive media, i.e. a frame of film, for a pre-defined period of time to scene illumination. The light is focused on the frame through a lens that has an aperture of a given, often variable, size. A shutter, situated behind the lens and in front of the film, opens for a selected period of time in order to permit the light to transit therethrough, illuminate and expose the film. As a result of being properly exposed and subsequently developed, the film undergoes a photochemical process, on a two-dimensional basis throughout the frame, that locally varies the optical transmissivity of each portion of the frame in proportion to the amount of illumination that reaches that portion of the frame from a corresponding portion of the scene, thereby producing, depending upon whether reversal or negative film is used, either a two-dimensional positive or negative optical image of the scene. As such, tonal variations that appeared in the scene are captured in the frame of the film. Photographic prints are often made from negatives, while transparencies (commonly referred to as "slides") are made from positives.
Though this overall process, which relies on the use of silver halide as a photosensitive reagent in film, has basically remained unchanged over many years, this process is highly non-linear and subject to a great many variables which significantly complicate its use. In particular, exposure (E) is defined, under a standardized definition, as being a product of the illuminance (I) multiplied by the time (t) during which the film is exposed to this illumination. In this regard, see specifically ANSI (American National Standards Institute) standard PH 3.49-1971 "American National Standard for General Purpose Photographic Exposure Meters" (re-affirmed in its entirety with no modifications in 1987 as ANSI standard PH 3.49-1987) [hereinafter referred to as ANSI standard 3.49-1987], and also ANSI standard PH 2.7-1986 "American National Standard for Photography--Photographic Exposure Guide" and specifically page 13 thereof. In a camera, the combination of two settings, namely lens aperture (size of the lens opening) and shutter speed (time during which the shutter remains open), primarily defines a particular exposure. Unfortunately, lens aperture and shutter speed define more than just an amount of exposure, these settings also dramatically affect picture (hereinafter including both prints and transparencies) quality and hence must be judiciously chosen in each photographic situation; otherwise, a picture (also referred to hereinafter as an image) having inferior quality will result.
Skilled photographers often experience difficulties in choosing the proper photographic settings under certain lighting conditions, e.g. lens aperture and shutter speed settings, selection of lens focal length, use and amount of flash illumination. These situations include, e.g. photographing a scene with a relatively thick subject (i.e. one necessitating a lens aperture setting that provides a sufficiently wide depth-of-field) under relatively low-light and particularly without the aid of either a flash unit or a tripod (or other similar device to hold the camera steady during an exposure). While certain lighting conditions are so extreme that they simply can not be handled by even a professional photographer--such as the above low-light condition but also with use of a telephoto lens that has a relatively long focal length, the vast majority of scene lighting conditions fortunately do not fall in this category. Nevertheless, from time-to-time actual photographic conditions may present sufficient difficulties to effectively frustrate the ability of an amateur photographer to take a picture of acceptable quality. In fact, for many inexperienced amateurs, choosing lens aperture size and shutter speed settings amounts to little more than mere guesswork, through which the probability is high that an amateur will select wrong settings and quickly become frustrated. Frustration, if it occurs sufficiently often, leads to dis-satisfaction, which in the context of an amateur photographer often means that that photographer will simply stop taking pictures and turn to other leisure activities which he or she believes to be less trying and more satisfying than photography. Since amateur photographers constitute a major portion of the photographic market, including both equipment and film, their continued satisfaction is essential to the photographic industry.
Having recognized this fact, the art has for many years pursued a goal of developing a camera that, over its lifetime, will produce more pictures that exhibit at least an acceptable and preferably higher level of quality than those resulting from cameras heretofore in use while, at the same time, relieving the photographer of the tedium and difficulty associated with choosing the photographic settings appropriate to a current lighting condition.
Hence, over the years, considerable activity has occurred in the art to provide cameras that automatically select a lens aperture size and/or shutter speed appropriate for a current scene being photographed. However, many of these automated cameras have uniformly based their exposure settings on strict adherence to the ISO/ANSI exposure standards. By doing so, these cameras provide a level of quality that, for a number of photographic conditions, is simply unacceptable. For ease of reference, these automated cameras will be referred to hereinafter as "ISO/ANSI" based automated cameras.
In essence, with such ISO/ANSI based automated cameras, once the value of one exposure parameter (such as shutter speed) is selected, a value of the other parameter (e.g. lens aperture) is dictated by that which would be required to produce a so-called ISO "normal" exposure of the scene being photographed. For example, in many inexpensive single mode and expensive multi-mode ISO/ANSI based automated cameras known in the art [the latter including those which can operate in shutter priority mode (where the photographer manually selects the shutter speed and the camera selects the lens aperture size), aperture priority mode (where the photographer manually selects the lens aperture size and the camera selects the shutter speed), and/or program mode (where the camera selects both the shutter speed and lens aperture size)], once one exposure parameter setting is fixed, the other parameter setting (e.g. lens aperture size or shutter speed, respectively) is selected by substituting the former parameter setting, along with the ISO (ASA) film speed, into a standard ISO metering equation and solving for a value of the latter parameter. The camera then simply sets the shutter speed and lens aperture mechanisms to the corresponding parameter values and then activates the shutter to capture an image of the scene.
In this regard, a "normal" exposure is defined by the ISO/ANSI standards as the lowest log exposure value, i.e. a single point--the so-called "normal" exposure point, on an exposure vs. density characteristic curve for each layer of a film in use that, in terms of faithful tone reproduction, produces an "excellent" quality image on that layer. By contrast, the ISO (ASA) film speed is defined from the exposure necessary to produce a specific value of image density on each layer of the film. Given the value of the "normal" exposure point for each such layer and associated standard exposure definitions for the film as a whole, then pairs of lens aperture and shutter speed settings that will each produce an ISO "normal" exposure can be readily determined by substituting the values for ISO (ASA) film speed and scene luminance into the ISO standard metering equation and calculating the results. See, specifically, ANSI standard PH 2.27-1988 "American National Standard for Determination of ISO (ASA) Speed of Color Negative Films for Still Photography" and ISO standard 588-1979, with the former ANSI standard adopting the latter ISO standard for determining the film speed; and the ANSI standard 3.49-1987, particularly page 21 thereof for the ISO standard metering equation; as well as D. M. Zwick, "The Technical Basis of Photographic Speed Determination or What is a Normal Exposure", SMPTE Journal, Vol. 88, No. 8, August 1979, pages 533-573 (hereinafter referred to as the Zwick publication). For ease of reference, the pertinent standards will be referred to hereinafter as the "ISO/ANSI exposure standards" with an exposure defined by these standards being referred to hereinafter as synonymously either an ISO "standard" or normal exposure and the normal exposure point being referred to as the ISO normal exposure point. From these definitions and use of the standard metering equation, the ISO normal exposure point occurs at higher density and exposure values on the log exposure vs. density curve than those associated with the ISO (ASA) speed point.
Since the ISO/ANSI standards are not predicated upon actual scene content, but rather for example on scene luminance, the resulting exposure settings, in certain instances, will not coincide with the actual requirements of the scene; consequently producing a rather poor quality image in these instances. For example, if a photographer were to select a shutter speed (such as through operation of an ISO/ANSI based automated camera in a shutter priority mode) to photograph a scene with a relatively thick subject, then the camera, though use of an ISO/ANSI standard metering equation and the speed of the film, would select a lens aperture that will produce an ISO normal exposure. Unfortunately, since this aperture selection is made without consideration of the actual scene content, the resulting lens aperture may not provide sufficient depth-of-field to properly cover the entire subject thickness. Hence, in the resulting photographed image, peripheral portions of the subject may appear out-of-focus and blurred. Moreover, if the photographer were to manually select a lens aperture (such as through operation of the camera in an aperture priority mode), then the resulting shutter speed for an ISO normal exposure may be inadequate to fully compensate for actual or expected camera shake given the size of the lens in use and the actual steadiness (or lack thereof) of the photographer--thereby resulting in a completely blurred and hence ruined image. In addition, owing to simple inexperience, an amateur photographer, when operating the camera in either the aperture priority or shutter priority mode, may often respectively select either a lens aperture size that simply provides insufficient depth-of-field for a given subject thickness or a shutter speed that is insufficient to fully accommodate actual or expected camera shake; in either case, such an errant setting would produce a poor quality image.
In view of the poor attendant image quality that often results from strict adherence to the ISO/ANSI standards under certain photographic conditions, efforts underway at the present assignee have resulted in the recognition that, contrary to long-standing and widely held conventional wisdom, these standards are not sacrosanct and should be intentionally violated where, based upon actual scene requirements and film quality characteristics, improved image quality will likely result. In this regard, U.S. Pat. No. 5,049,916 (issued Sep. 17, 1991 to W. R. O'Such et al--hereinafter referred to as the O'Such '916 patent and commonly assigned to the present assignee hereof) describes an automated exposure control system that, where necessary, intentionally violates the ISO/ANSI exposure standards to provide exposure (and, where suitable, flash) parameter settings that, based upon meeting actual scene requirements and use of film quality characteristics, will yield highly acceptable images under a wide variety of photographic conditions. In fact, the resulting image quality produced by this system is consistently much higher than that attainable through strict adherence to the ISO/ANSI exposure standards.
Specifically, for a scene being photographed, the exposure control system described in the O'Such '916 patent: (a) determines initial exposure settings (e.g. shutter speed and lens aperture and, where appropriate, flash parameters) that are necessary to provide a baseline, typically ISO normal, exposure of that scene; (b) ascertains corresponding exposure settings (and again, where appropriate, flash parameters) that actually meet the scene requirements, such as, e.g., expected or actual camera shake induced image blur and required depth-of-field given actual subject thickness in the scene; (c) assesses, in response to differences between the initial and corresponding exposure settings, whether any extra system speed exists and, if so, the amount of extra system speed which is available for use in photographing the scene; and (d) finally, where possible, properly utilizes that extra system speed in a pre-defined prioritized incremental manner to vary the baseline exposure settings (and again, where appropriate, flash parameters) to provide an exposure of the scene that produces a desired level of quality--e.g. in excess of the quality that would result from strict adherence to the ISO/ANSI standards.
By utilizing the ISO/ANSI exposure settings as effectively a baseline point from which to diverge (rather than as final settings as in conventional "ISO/ANSI" based automated cameras) and then properly deviating from these settings where necessary to satisfy actual scene requirements, the system described in the O'Such '916 patent advantageously yields a greater number of images with an acceptable and generally higher level of quality than does adherence to the ISO/ANSI standards.
However, we have discovered that the system described in the O'Such '916 patent contains an implicit underlying assumption that, if ignored, can artificially limit the quality improvement attainable through use of this system.
Specifically, as with most imaging systems, the system described in the O'Such '916 patent assumes that an output image will be viewed on a single standard display size, e.g. a 31/2" by 5" (approximately 8.9 cm by 12.7 cm) photographic print, and at a standard viewing distance therefrom. The exposure settings are then optimized using parameter values that are based upon this assumption. However, in practice, photographic images are not necessarily enlarged to just one standard display size.
In this regard, images situated on photographic negatives are often enlarged across a variety of different display sizes. Oftentimes, prior to photo-finishing, an individual may elect to have an image on a particular negative enlarged from one standard size, e.g. such as 31/2" by 5", to another, such as 8" by 10" (the latter being approximately 20.3 cm by 25.4 cm), or even to a non-standard size. Furthermore, with the possible advent of non-standard (pseudo) focal length photographing modes, i.e. pseudo-panoramic and pseudo-telephoto, we foresee an increased demand for non-standard sized prints in the near future. In particular, through various information exchange processes that have recently been developed in the art to exchange data recorded by the camera with downstream photo-finishing equipment, a photographer should be able to store data on the film that, at the time of image capture, will specify the desired display type and/or focal length photographing mode of a resulting print. This data will likely be stored on the film in the vicinity of each frame and will specify the desired display size and/or the focal length photographing mode to use in enlarging the image, i.e. as a normal print or as either a pseudo-panoramic or pseudo-telephoto image. In use, once the film is developed and then ready to be printed, this data will be subsequently read during enlargement by a photo-printer and will appropriately control its operation (e.g. setting a proper reproduction magnification ratio) to yield the desired display size and focal length photographing mode. With respect to the photographing mode, for a pseudo-panoramic image, the image on the negative could be enlarged (with or without vertical cropping) using a particular aspect ratio that greatly favors a horizontal direction to form, for example, a 3.5" by 10" (approximately 8.9 cm by 25.4 cm) print; while for a pseudo-telephoto image, the image on the negative could be cropped both horizontally and vertically to yield a central portion of the image that, in turn, could be appropriately enlarged to a specific size. The appropriate cropping could also occur through the lens at the time of image capture. For further details of cameras that have pseudo-panoramic and pseudo-telephoto capabilities, see illustratively U.S. Pat. Nos. 5,025,275 (issued to N. Taniguchi et al on Jun. 18, 1991--hereinafter referred to as the Taniguchi '275 patent); 5,003,340 (issued to D. M. Harvey on Mar. 26, 1991) and also assigned to the present assignee hereof); 4,860,039 (issued to Y. Hata et al on Aug. 22, 1989); 4,583,831 (issued on Apr. 22, 1986); and Re. 32,797 (issued on Dec. 6, 1988--the latter two patents both being issued to D. M. Harvey and assigned to the present assignee hereof). While both pseudo-panoramic or pseudo-telephoto type images represent just one exemplary situation that may yield non-standard display sizes we expect that the increasing ease with which enlarging equipment will be able to generate a wide variety of different print sizes (both standard and non-standard) will only heighten the demand for producing images across a broad range of display sizes.
Unfortunately, while use of non-standard display sizes does affect perceptual image quality, this factor is not taken into account through the optimization process described in the O'Such '916 patent. Consequently, we have determined that, while the resulting image quality that is attained through this optimization process for non-standard display sizes and viewing distances is still quite acceptable, i.e. at least equaling and usually exceeding that which would result from adherence to the ISO/ANSI standards, further improvements in image quality may well be possible if this optimization process could be modified to properly account for this factor.
In particular, to determine a lens aperture size that meets the scene requirements, that aperture size must, at a minimum, impart sufficient depth-of-field to a resulting photograph to clearly capture the entire thickness of a subject. As described in the O'Such '916 patent, near and far subject distance measurements (or e.g. statistical assumptions therefor) are used to determine the required depth-of-field to faithfully photograph an image of a scene. Thereafter, an appropriate maximum lens aperture opening is determined as a well known function of not only the measured near and far subject distances and the focal length of the lens in use, but also of a so-called "blur circle criteria" (also commonly known as the "permissible circle of confusion"). As is well known, for any focal length lens and an aperture setting therefor, there is only one distance from the lens at which that lens will perfectly focus light emanating from any point in the object field onto a resulting focal plane. Given this, the blur circle criteria (when multiplied by an appropriate reproduction magnification ratio) defines a diameter of a circle on a print that when viewed at a given, e.g. standard, viewing distance, will generally appear as a single point to a human observer. Hence, any blur that extends over an area on the print equal to or less than that which is encompassed by this circle is not likely to be visible at the standard viewing distance to a naked eye. In essence, through use of the blur circle criteria and the measured near and far subject distances, a lens aperture setting can be defined as that which will capture an image with tolerable amounts of blur across the full extent of the required depth-of-field. Accordingly, the resulting portions of the image that are situated within the required depth-of-field will appear, at the standard viewing distance, clear and sharply focused.
Generally in camera design and in the exposure control system described in the O'Such '916 patent, the blur circle criteria itself, for e.g. amateur photographic cameras, is taken to be a fixed value, for example 0.002" (approximately 0.005 cm) on a negative for type 135 film. For images with increased sharpness, such as those taken with professional cameras, this criteria may be taken to be 0.001" (approximately 0.0025 cm). In any event, for a standard 31/2" by 5" print taken with an amateur type camera, a negative is enlarged typically by a printing magnification factor (also referred to herein as a "reproduction magnification ratio") of 3.9-4.times. resulting in an 0.008" (approximately 0.020 cm) blur circle on the print. For a 0.001" blur circle on the negative, the resulting blur circle on this standard sized print would be 004" (approximately 0.010 cm). Image blur of this magnitude is generally not visible to a human observer when this print is held at a standard viewing distance, such as for example 10" (25.4 cm) or so. In this regard, see pages 160-161 of L. Stroebel et al, Photographic Materials and Processes (.RTM.1986: Focal Press, Boston) for further details. Now, as the reproduction magnification ratio increases (such as through use of relatively small sized negatives, e.g. type 110 film which requires a ratio of approximately 7.2.times. for a 31/2" by 5" print rather than type 135 film which requires a ratio of 3.9-4.times., or by producing increasingly large prints from a common sized, e.g. type 135, negative), then to maintain the same size blur circle and hence image sharpness on the print, the blur circle criteria for the negative must decrease accordingly.
Unfortunately, a fixed number is used as the blur circle criteria used in the O'Such '916 patent regardless of the actual display size. Accordingly, the exposure control system described in this patent may not always produce optimum exposure (and, where suitable, flash) settings for prints that have a non-standard display size, which, in turn, will limit the quality improvement attainable through use of this system.
While an attempt has been made in the art, specifically that shown in the Taniguchi '275 patent, to limit image degradation (though in an entirely different exposure control system than that described in the O'Such '916 patent) attributable to increased image noise (graininess) at relatively high reproduction magnification ratios, this attempt does not appear to fully counter the adverse affects on changes in image quality that result from changes in display size. In particular, the Taniguchi '275 patent teaches limiting the reproduction magnification ratio, whenever a photographer, using a relatively high speed film (such as over ISO (ASA) 400 speed) with correspondingly relatively coarse particles, selects a relatively large "pseudo focal length".
Consequently, a need still exists in the art to provide an automatic exposure control system for use in a camera that not only further reduces the tedium, difficulty and guesswork, associated with using currently available automated cameras, to take pictures under a wide variety of different lighting conditions but also provides pictures that possess a further increase in their overall level of quality than that attainable through such exposure control systems now known in the art. In that regard, a specific need now exists for an exposure control system that, not only automatically selects appropriate exposure settings based upon scene requirements and film quality characteristics for an image being captured, such as the methodology which occurs in the system described in the O'Such '916 patent, but also properly compensates these settings for changes in the resulting display size of that image and/or in the focal length photographing mode associated therewith.